Currently, an NG-PON (Next Generation Passive Optical Network) is a research hotspot in the field of communications technologies. The NG-PON includes a 10 G PON (Passive Optical Network), a 10 G symmetric PON, and the like. An OLT (Optical Line Termination) is a central office device in a PON communications system, and is mainly used to: send Ethernet data to an ONU (Optical Network Unit) in a broadcast manner, perform a ranging process, and allocate a sending slot to the ONU, that is, control a start moment and an end moment of sending data by the ONU. The ONU is user equipment in the PON communications system, and is mainly used to: receive the Ethernet data broadcast by the OLT, respond to the ranging process performed by the OLT, and send data according to the sending slot configured by the OLT. One of current research issues is how to make the NG-PON compatible with an ONU (Optical Network Unit) in an EPON (Ethernet Passive Optical Network) or a GPON (Gigabit Passive Optical Network) deployed in a previous-generation technology. In this case, an OLT in the NG-PON needs to receive not only a signal sent by an ONU in the NG-PON, but also a signal sent by an ONU in the EPON.
Each ONU in the PON communications system performs access by means of time division multiple access. A signal received by the OLT is unexpected. For receiving of an unexpected signal, because rates of all unexpected packets are different, signal amplitudes and phases of all the unexpected packets are different from one another. Therefore, an optical receiving component of the OLT determines a rate of the ONU according to a signal characteristic of a received unexpected packet, and then adaptively adjusts a reception parameter of the optical receiving component according to the rate.
In the PON communications system, a requirement for a time sequence of data receiving is extremely high. However, duration of an unexpected packet is quite short. It is quite difficult for the OLT to detect a rate of the unexpected packet and then adjust a reception parameter of the optical receiving component in such a short time. Consequently, the OLT is likely to fail to adjust the reception parameter of the optical receiving component in time when the unexpected packet arrives, and therefore cannot correctly receive data.